Quantification of Effect of Enforced Cyclic Movement and Regional Exposure Factors on Weatherability of Construction Sealants

ABSTRACT: This paper presents information on the weatherability of con­struction sealants based on a newly developed test specimen design that allows simultaneous exposure of the sealant to forced compression and ex­tension movement in a single specimen. In this study, exposure to cyclic movement and weathering is carried out simultaneously. Furthermore, an evaluation method for surface cracks induced by weathering is presented that allows an assessment of the overall “degree of degradation,” a single number characterizing the state of degradation of the sealant surface. In order to study the effects of the extent of extension and compression as well as the regional exposure factors on the degree of degradation, twelve seal­ants were exposed to outdoor weathering for four years at three exposure sites, located in the northern, central, and southern areas of Japan. The evaluation of surface cracks was carried out according to the rating provided in ISO 4628-4, with the modification that new rating criteria were introduced to evaluate minute cracks. A mathematical equation determining the “degree of degradation” was obtained for each sealant, which is based on a compo­nent reflecting aging under static condition and another component reflecting the dynamic conditions induced by mechanical movement and regional ex­posure factors. This equation provides a reasonable relationship between the experimental observation and calculated degradation over the exposure period.

KEYWORDS: sealant, weatherability, regional factor, joint movement, out-door exposure

Introduction

A construction sealant is a material used to maintain the waterproof and air­tight functions of a joint over the long term, and the weatherability of the sealant is an important performance criterion for maintaining these functions. Although the degradation of sealants in the outdoors proceeds by UV irradia­tion, heat, water, and many factors in general, the dynamic movement to which the sealant is exposed in actual joints accelerates the degradation.

The quantification of the surface degradation on a particular exposure site [1] was reported by using the newly devised test specimen [2].

The purpose of this study is to evaluate the extent to which the geographic location of exposure influences the surface degradation by carrying out the exposure test at three different sites in Japan.